1. Field of the Invention
This invention relates to a solid titanium catalyst component and an olefin polymerization catalyst prepared from the same. More particularly, the invention relates to a process for preparing a solid titanium catalyst component, such a catalyst component as prepared by the process, a preliminary olefin polymerization catalyst and an olefin polymerization catalyst both prepared from such a catalyst component, and a process for producing polyolefins using such catalysts.
2. Description of the Prior Art
A Ziegler-Natta catalyst comprising a titanium catalyst component and an organoaluminum compound have been in wide use as an olefin polymerization catalyst. It is already known that a catalyst which is prepared from a solid titanium catalyst component comprising a titanium compound supported on a solid carrier has high polymerization activity. In particular, it is also known that a catalyst which is prepared from a solid titanium catalyst component comprising a titanium compound supported on a solid halogenated magnesium compound has high polymerization activity, but also the catalyst provides highly stereospecific polyolefins in high yields when it is used for the polymerization of alpha-olefins having at least three carbon atoms such as propylene or 1-butene.
The solid titanium catalyst component comprising a titanium compound supported on a solid halogenated magnesium compound may be prepared by contacting a halogenated magnesium compound, a titanium compound and an electron donor with each other.
A process for an olefin polymerization using such a solid titanium catalyst component is known, as disclosed in Japanese Patent Application Laid-open No. 58-83006. According to the prior art, a solid titanium catalyst component is prepared by use of a hydrocarbon solution of a magnesium compound, a titanium compound which is per se liquid such as titanium tetrachloride and an electron donor. An olefin polymerization catalyst is then prepared from the solid titanium catalyst component, an organometallic catalyst component and an organosilicone catalyst component. The prior art uses a certain compound such as an acid anhydride in combination with a polybasic carboxylic acid ester or a polyhydric alcohol ester as an electron donor when the solid titanium catalyst component is prepared.
The hydrocarbon solution of a magnesium compound is prepared usually by solubilizing a magnesium compound which is solid at normal temperatures such as magnesium chloride with a solubilizing agent, if necessary, in a hydrocarbon solvent. A preferred example of the solubilizing agent is an alcohol such as 2-ethylhexanol.
More specifically, according to the prior art, the solid titanium catalyst component is prepared by first contacting a solution of a magnesium compound with titanium tetrachloride in the presence of an electron donor to form a suspension which contains the resultant solid material; the solid material is separated from the suspension; and then the solid material is again contacted with titanium tetrachloride under heating.
As mentioned above, the polymerization of olefins in the presence of a catalyst prepared from the solid titanium catalyst component together with an organometallic catalyst component and an organosilicone catalyst component provides polyolefins in high yields. In particular, the polymerization of alpha-olefins having at least three carbon atoms provides highly stereospecific polyolefins in high yields. In addition, the resulting polyoefins have a small content of finely divided polymer powder as well as narrow particle distribution and high bulk density.
The known olefin polymerization catalyst which is prepared by a method as described above and contains the solid titanium catalyst component has a high performance in many respects, that is, in respect of polymerization activity, and stereospecificity and particle properties of the resulting polymers, as above set forth. However, in recent years, there is a strong demand for a solid titanium catalyst component for use in the preparation of an olefin polymerization catalyst which reduces the amount of finely divided polymer powder produced.
Therefore, it is an object of the invention to provide a solid titanium catalyst component for use in an olefin polymerization catalyst which has high olefin polymerization activity, and in particular, for use in an alpha-olefin polymerization catalyst which provides polyolefins having high stereospecificity and bulk density in high yields with a reduced amount of finely divided polymer powder produced when alpha-olefins having at least three carbon atoms are polymerized.
It is a further object of the invention to provide such a solid titanium catalyst component, a preliminary olefin polymerization catalyst and an olefin polymerization catalyst both comprising the solid titanium catalyst component and a process for the polymerization of olefins using such catalysts.